Recovery of rubber.



' LINDE,

UNiTED STATES PATENT HAROLD 'r; G. VAN DER 1.1mm; on NEW YORK, N. Y.

or RUB ER.

RECOVERY 979,902. sneciflcationjot Letters Patent. i :No Drawing.

To all whom it may concern:

Be it known that I, HAROLD T. G. VAN DER a subject of the King of GreatBritain, residing in the borough of Manhattan,.city, county, and Stateof New-York, have invented certain new and useful Improvements inRecovery of Rubber; and I do hereby declare the following-to be a full,clear, and exact 'description of the invention, such as will enableothers skilled in the art to which it appertains to make and use thesame.

My invention relates to certain new and useful improvements in method ofseparating particles ofrubber from substances with which they areassociated.

In its broader aspect, as will herelnafter appear, the invention isapplicable generally to the separation of particles of rubber, whethervulcanized or unvulcanlzed, from the remaining ingredients ofmixtures inwhich they are present. The invention is of special service, however, inthe recovery of rubber from trees, plants, shrubs, roots, vines or thelike, wherein the rubberv is contained in the texture of the vegetablesource, or as a coagulable latex, as, for instance, in the guayule shrubwhich grows in arid re gions in northern Mexico and southern Texas, andwhich has necessitated, for various reasons, a special treatment for theeconomical extraction of its rubber contents.

In the guayule shrub,-the rubber present is accompanied by aboutone-fourth or more of its weight of a resinous matter containing oxygen,and the associated-rubber and resin lie mainly inthe outside [structuresof the shrub (chiefly in the bark), probably serving to prevent undueevaporation of the scanty juices of the plant duringthe prolonged dryseasons. almost invariably treated as follows: It is first finelydivided by crushers or cutters, and the resulting crumb is placed in apebblemill. The pebbles and the finely divided shrub are then coveredwith water; the door of the mill is closed, and the pebble mill isrotated, so that the falling and rolling pebbles will squeeze and rubthe crumbin the body of the water below its surface. This action notonly disintegrates the corky and woody parts of the plant, dividing theminto smaller and smaller frag- The shrub is now ments but the action onthe rubber is of an opposlte character, due to the property of teristicof this substance. By reason of this property, whenever the pebblespress two or more particles of rubber together, they coalescecompletely, forming a larger particle,

ticles will almost, if not entirely, separate itself from the rest ofthe material, and by this stage is reached, the mill is stopped, the.

door opened, and the contents, less the pebbles, 1s emptied intoswimming or flotation of the rubber floats, and most of the woody andbarky matter (containing much of the resin) sinks. The water in thepebble mill also serves to kee down the temperature resins.

The material which sinks inthe flotation tanks is known in the art assinkers or rubber bagasse. Even in the most up-todate factories aboutone-twelfth to oneeighth of the "rubber often remains entangled with.the sinkers or bagasse, according to the condition of the shrub, andheretofore has been commerciallyunrecoverable. The rubber particles thusentangled in the bagasse are in small pieceswhichadhere to the particlesof wood, either through the natural adhesivene'ss of the-rubberv itself,or by the joint effect of this adhesiveness with wood; or, sometimes thewoody fiber is driven into or through the particles of rubher, andsometimes the rubber adheres to small particles of foreign matter, suchas der the boilers in the plant, but, because of int-1t is an expensivefuel and to burn it tanks. Here, in water, by gravitation, .most

'thejpresence of the particles of rubber there- Patented Dee. 27, 1910.Application filed January 8, 1910. Serial No. 536,980.

welding or regelation that is a char'acand as soon as the portion of theshrub containm' said particles is relieved of the pressure 0 thepebbles, each of these rubber parreason of its specific gravity beingless than that of water, will rise to' the surface of the below thesoftemng temperature of the the extreme stickiness of the resin in thesand; The usual method of disposing of this rubber bagasse' is to burnit as fuel unim'eansa' great loss to themanufacturer.

For the recovery of particles of [rubber thus entangled in the sinkersor rubber bagasJe, it is to be borne in mind that the two bodies whichwe desire to separate, in this instance, are: (1) Rubber (plus resin),slightly lighter than water, with comparatively sli ht buoyancy therein;(2) hard woody an barky matter (plus resin), most of which will notfloat, if freed from air bubbles, even in a liquid having a specificgravity of 1.2, or even in a saturated solution of common salt.

Although, in specialcases, I may employ a liquidof greater specificgravity than water, and even a saturated solution of common salt, Iprefer to use natural-water, of the usual specific gravity, as the bestand most easily available liquid in which to conduct the separation, forthe reason that the woody and barky matter already possesses a specificgravity suiiiciently differentiated from that of water for all practicalpurposes and because (unlike a saturated solution of common salt, forexample), it leaves no residue prejudicial to the value of the residueas a fuel after the rubber particles have been eliminated. I may also,in various ways, make the woody and barky particles heavier, but formost purposes, ordinary water-logging will be all that will be attemptedin this regard. Primarily, therefore, my invention is directed towarddecreasing the specific gravity of the rubber particles, thereby makingthem lighter and ratin fluid, so that, when; the mass-is subjecte to theaction of a separating liquid of suitable specific gravity, such aswater, the diflerence in the specific gravity between the buoyant rubberparticles and the remaining ingredients of the mixture will be so farincreased that a ready se aration will take place, the completeness othe separation be ing, in some instances, enhanced by stirring the mass.In order to thus decrease the specific gravity of the particles ofrubber and therefore increase their buoyancy or lightness, I subject themass to the action of an intumescent, that is, an agent which will swellthe rubber particles so as to decrease their weight per unit of. bulk.This may be effected either through the agency of any suitable solvent,acting upon the rubber particles under suitable conditions, orthroughthe agency of a gas or liquid adapted to be occluded in therubber.

The conditions of use of the intumescent, in order to have the effectcontemplated by my invention, will require that its employ ment shall belimited to the first stage of the swelling action, 2'. e., to that stagewherein the intumescent, upon coming into contact with the rubberparticles, causes them to swell considerably without, however, goingover into the liquid condition of full solucompounds and derivatives. Iprefer to use thus increasing their buoyancy in the sepation. Thiscondition is commonly reco nized as a stage in the action of solvents ona vegetable and animal colloids in general. j

Rubber is very easily swelled by bringing it into contact with a greatmany substances g of an intumescent character. The rubber first swellsgreatly, as the intumescent diffusesthrough the mass, and if theintumescent be also a solvent it may slowly a proach the liquid state,as more of the so vent is added, until, at last, with sufficient timeand stirring, the rubber enters intoa state of pseudo-solution, theexact nature of which has not been fully determined. In order to enablethese intumescents to diffuse through the substance of the rubber to thebest advantage they should be, in most instances, in the liquid,vaporous or gaseous state at the temperature at which the operationtakes, place. In fact, in order not to break down 5 the very unstableand highly polymerized rubber molecule, the operation should beconducted at, or nearly at, the ordinary temperature of the atmosphere(somewhere between, say, F. and 100 F. preferably), although theselimits may be extended.

Among the solids, liquids and gases that may be used as the intumescentor swelling agent for the rubber particles, I may enumerate thefollowing:

1. All the volatile and liquid substances. of the paraflin series, frommarsh gas to the heavy lubricating oils, with many of their this classof substances, in most instances, and more particularly one of thespecies thereof, 2'. 0., the petroleum distillates, as I willhereinafter more fully appear.

2. The olefines, their compounds and derivatives.

3. Benzene (C H and its homologues.

4. Phenol, its homologues, compounds and derivatives.

5. Essential oils in general.

6. Fixed fatty oils. I

7. The higher fatty acids.

8. Some alcohols, ethers, compound esters, aldehydes, ketones, etc.

9. Turpentine, resin spirit, resin oil etc., including their compoundsand derivatives.-

l0. Chloroform and similar (analogous) bodies.

11. Carbon disulfid, carbon tetrachlorid.

12. Carbon dioxid, coal gas and other illuminating gas, carbon monoxidor hydrogen, because when occluded into rubber they lower its specificgravity by swelling it (No. 12 is obviously overlapped in part by Nos. 1and 2).

13. Anilin and some analogous bodies, their compounds and derivatives.

14. Heavy or dead oil of the gas works.

15. Light gas tar or petroleum tars and similar bodies.

v or even lighter.

' 16. Isoprene and many such bodies of the composition of O I-I C H andtheir polymers.

17. Creosote, and many other volatile and non-volatile products. a

I- have heretofore referred to the fact that the rubber bagassecontains, mainly in the woody and barky matter, besides the rubber, afurther large quantity of resin, this designation being herein employedto include a mixture of several acetone-soluble substances, besidesminor fractions of undetermined composition. It is, therefore, desirablethat the intumescent employed should be a better solvent for rubber thanfor resin. It is also desirable that any solvent intumescent employedshould neyertheless have a sufficient action upon the resin to soften itup slightly, so that, after the swollen rubber particles have beenseparated in the flotation tank, the softened resin Will act to betteradvantage, as'a binder, in briqueting the residue of woody and barkymatter,.for fuel purposes. I have found by experimentation that anintumescent uniting these desirable characteristics ispetroleum-distillate, as, for instance, any of the fractions rangingfrom kerosene to a spirit of 72 B.,

The most suitable petroleum-distillate fractions have the additionaladvantage that they are cheap, tolerably constant, easily obtained insufficient quantities, volatile and of low specific gravity, and

readily driven off by a heat not higher than \Vhen a mixture of that ofboiling water.

1 bagasse with water is subjected to vigorous agitation with a suitablequantity of one of thesebodies, the rubber very rapidly absorbs alargepart of the spirit, swells up, and comes to the top if the vessel beallowed to stand. When the agitation applied is sufficient, the rubberthus floating is found to be practically all that the bagasse contained.In practice, it is preferable to employ a kind of agitation that willboth mix the intumescent into and simultaneously disintegrate thebagasse, and to this end, the usual pebble mill may be employed withsatisfactory results. The water used in the pebble mill subservestheusual functions of a lubricant and a cooling agent to keep down thetemperature of the bagasse during the tumbling operation, and, while theamount of water used should be'suflicient for these purposes, it shouldnot be "employed in materially larger quantity, for the reason that itspresence naturally slows down the action by preventing free contact ofthe petroleum spirit and the rubber.

In practice, I have obtained satisfactory results by first dewateringthe rubber bagasse until it has a'consistency resembling that of wetsaw-dust or tea leaves that are sprinkled on a floor before sweeping. Ithen place the dewatered .bagasse in a revolving drum, sometimes, butnot necessarily,

adding pebbles or balls, to make up the usualpebble mill charge. Ameasured quantity of intumescent (say 62 B. naphtha) equal to aboutthree-quarters of a U. S. gallon, to one hundred pounds of the drybagasse (i. e., of the bagasse minus its moisture) is added, and thedoor of the drum is closed. The drum is then rotated, continuously oratintervals, until the desired swelling effect has been attained, whichwith an atmosphere at about 80 F., and a barbmetric pressure of between550 mm. and 650 mm.

takes about from one to four hours,,according to the character of thecharge and the proportions thereof. The door is then opened and thethoroughly mixed and disintegrated mass, minus the balls or pebbles, isthen thrown into a flotation tank containing cold water, and vigorouslystirred. On standing for a short time, nearly all the rubber, with onlya small quantity of Woody fiber, is found floating on the surface. Thisis skimmed off and the small amount of fiber which comes with it isseparated by wellknown methods. The solvent, of course, may berecovered, by simple means, from both the floaters and sinkers.

By means of my invention, therefore, the particles of rubber containedin the rubber bagasse of the ordinary method of rubber extraction fromtheguayule shrub and the like are recoverable economically, for whichreason the invention is applicable to the treatment of a material whichhas hitherto been rated as a waste product except for fuel purposes.Furthermore, the softening up of the resin, incident to the operation,causes the particles of the sinkers, after the water has been run offfrom the flotation tank, to be quite adhesive, so that they can bebriqueted Without a binder, or with a very small proportien of a binder,in which condition the briquets are in good mechanical shape for firing,and can be piled and allowed to dry, which is impossible with theflocculent baga sse itself. I have further ascertained and demonstratedthat the intumescent can be employed at an earlier stage of thetreatment of the shrub, to-Wit, when the original crushed shrub is beingsubjected led to the equeezing and rubbing action of the into theflotation tank and vigorously agitating it therein for a few minutes,substantially all of the particles of rubber will rise to the surface,together with a small quan tity of the woody fiber, and the main bodyportion of the woody fiber and barky matber of advantages overextracting it from Thus, it requires butusual practice.

' &

ter will sink to the bottom of the flotation tank in the form of bagassecontaining but a negligible quantity ofrubber, and adapted, by reason ofthe softening up of its resin, to be briqueted, as before. Thisinnovation in the method of extracting rubber. directly from theoriginal crushed shrub has a numthe rubber bagasse. one handling insteadof two, and permits a corresponding saving in apparatus v(especiallytankage apparatus) and the floor space therefor. In comparison with theusual pebble mill treatment, wherein an intumescent is not employed, ithas additional and striking advantages. For instance, in the treatmentof the original crushed shrub in the pebble mill, it is found that theamount of shrub charged in the mill may be considerabl the uration ofthe tumbling operation is reduced by one-half. Furthermore, it is onlynecessary to employ about one-twelfth, by weigth, of the pebbles used inthe old method, 2'. e., 334 pounds, instead of 4,000

pounds, and the amount of liquid employed in the pebble mill is reducedfrom about 1,250 pounds to about 400 pounds. Inasmuch as the powerrequired-for operating the mill is about one-fourth of that needed bythe old method, the total energy required for operating the mill is butone-eighth of the In addition to this, there is a considerable saving inwater and pumpingthe ordinary method requiring about 400 pounds or moreof water for every pound of dry rubber shipped, whereas this iscut downin the new method to probably onetenth of that amount. Finally, thesaving in plant and tankage is further supplemented by the production ofa good, dry, easily handled fuel, instead of a fluffy and inefiicientfuel containing usually about fifty per cent. of Water.

I have hereinbefore indicated that, in its broader aspect, the inventionis applicable generally to theseparation of particles of rubber, whethervulcanized or unvulcanized, from the remaining ingredients of mixturesin which they are present. One instance of this broader use is in theapplication of the invention to the reclaiming of rubber from old rubbershoes, vold rubber beltin hose, automobile tires, and the like, all 0which contain a large proportion of cotton or other similar fabric. Thisold waste rubber material, which forms a common market sta le, is sortedand ground up into a more or ess fine crumb, which is then treated withhot "dilute sulfuric acid, to destroy the fiber, which is useless formanufacturing purposes. The end-products of such reactions are wellknown, most of them being soluble bodies which are easily washed out. Avery large proportion of the cellulose is, however,

increased, while, at the same time,

only partially acted on, leaving a large mass of oxycelluloses andsimilar bodies, which are insoluble. As these bodies are usuallysomewhat slimy, and as the difference between their specific ravitiesand that of the rubber portion of t e mass is small, it has hithertobeen found diflicult to separate them cheaply and efficiently.

For the separation of the rubber particles from their admixture with theoxycelluloses and like constituents, the mixture, in a wet or moistcondition, 'similar to that of the rubber bagasse, may be tumbled anddisin teg'rated in a pebble mill in the presence of a suitableintumescent, as, for instance, naphtha or other likepetroleum-distillate,

and the swollen rubber particles are then to the bottom of the tank assinkers.

In connection with the foregoing description, it will be noted that inthe treatment of the original milled shrubs, I have had satisfactoryresults in employing from six to ten per cent. by weight of naphtha asthe swelling agent. For the treatment of the reclaimed rubber, even alesser amount (say 4% by weight) will sufiice. It is evident, however,that these quantities may be varied in individual instances according tothe particular condition of the material treated, which is alwayssubject to more or less variation.

What I claim is:

1. In the art of separating particles of rubber from mixtures in whichthey are contained, the method of increasing the buoyancy of the rubberparticles, for the purpose described, by subjecting them to the actionof a specific-gravity lowering intumescent; substantially as described.

. ries, substantially as described.

4. In the art of separating particles of rubber from mixtures in whichthey are contained, the method of increasing the buoys ancy of therubber articles, for the purpose described, by su jecting them toagitation in the presence of a specific-gravity lowering intumescent;substantially as described. I a

5. In the art of separating particles of rubber from mixtures in whichthey are c0ntained, the method of increasing'the buoyancy of therubber-particles, for the purpose described, by subjecting them toagitation in the presence of water and a specific-gravity action of aspecific-gravity lowering intu-r subjecting the mescent andsimultaneousla;

rubbing action mixture 'to a squeezing an in the presence of water;substantially as described. v

7. In the art of separating particles of rubber from mixtures which alsocontain resin,the method of'increasing the buoyancy of the rubberparticles without materially increasing'the buoyancy of the resin, whichconsists in subjecting the mixture to the action of a substance whichhas a greater swelling effect upon rubber than upon resin; substantiallyas described.

8. In the art of separating particles of rubber from mixtures which alsocontain resin, the method of-increasing the buoyancy of the rubberparticles withoutmaterially increasing the buoyancy of the resin, whichconsists in subjecting the mixture to the action of a. substance whichhas a greater swelling and specific-gravity lowering effect upon rubberparticles than upon resin, but which is a sufiicient solvent of resin tosoften up the resin and enable it to act as a binder in briqueting themass after the separation of the swollen particles of rubber;substantially as described. V t

9. In the art of separating particles of rubber from a mixturecontaining them, the

' mass to the separatin method of increasing the buoyancy of the rubberparticles, which consists in swelling the rubber particles by subjectingthem to the swelling action of a petroleum distillate; substantially asdescribed.

10. In the art of separating particles of rubber from a mixturecontaining them, the method of increasing the buoyancy of the rubberparticles, which consists in swelling the rubber particles by subjectingthem to the swelling action of a petroleum distillate in the form ofvapor; substantially as described.

11. In the art of separating particles of rubber from mixtures in whichthey are contained, the method'of decreasing the specificgravity of therubber particles and effecting their subsequent separation, whichconsists in subjecting them to the action of a specificg'ravity loweringintumescent, thereby increasing their buoyancy, and subjecting theaction of a liquid while the rubber partlcles are still in the conditionof increased buoyancy; substantially as described.

12. In the art of separating particles of rubber from a mixturecontaining them, the method of increasing the buoyancy of the rubberparticles and effecting their subse quent separation, which consists insubjecting themto the swelling action of a specificgravity loweringsolvent, and then subjecting the mixture containing the swollen particles of rubber to gravity separation in a liquid; 'substantiall asdescribed.

13, In the art 0 separating particles of rubber from a mixturecontaining them, the method of increa'sin the buoyanc of the rubberparticles an efi'ecting thelr subsequent separation, which consists insubjecting them to the swelling action of a specificgravity loweringintumescent, and then separating out the swollen rubber particles bysubjecting the mass to agitation in the presence of a separating liquid;substantially as described.

14. In the art of separating particles of rubber from a mixturecontaining them, the method of increasing the buoyancy of the! rubberparticles and effecting their subsequent separation, which consists insubjecting them to the swelling and specific-gravity lowering action ofa solvent, and then separating out the swollen rubber particles bysubjecting the mass to agitation in the presence of a separating liquid;substantially as described.

15. In theart of separating particles of rubber from mixtures in whichthey are contained, the method of increasing the buoyancy of the rubberparticles and ofeffecting their subsequent separation,.w'hich consistsin subjectingthe rubber particles to the swelling action of aspecific-gravity lowering intumescent water-logging the otheringredients of t e mixture, and subjecting the mixture of swollen rubberparticles and water-logged particles to the separating action of aliquid; substantially as described.

16. In the art of separating particles of rubber from mixtures in whichthey are contained, the method of increasing the buoyancy of the rubberparticles and. of effecting theinsubsequent separation, which consistsin subjecting the rubber particles to the swelling action of aspecific-gravity lowering solvent, water-logging the other in- 120gredients of the mixture, and subjecting the mixture of ,swollen rubberparticles and water-logged particles to the separating action of aliquid; substantiallyas described.

17-. In the art of separating particles of rubber from mixtures in whichthey are'contained, the method of increasing the buoyancy of the rubberparticles and of eflecting their subsequent separation, which consistsin subjecting the rubber particles to the acthe rubber particles, andthen effecting the ,ancy of the rubber particles and of effectingflotation; substantially as described.

tion of a specific-gravity lowering int-unlescent, and then subjectingthe mixture to the separating action of a liquid containing a suitablesoluble material to increase its specific gravity; substantially asdescribed.

18. In the art of separating particles of rubber from mixtures in whichthey are contained, the method of increasing the buoytheir subsequentseparation, which consists in subjecting the rubber particles to theaction of a specific-gravity lowering intumescent, water-logging theother ingredients of the mixture,-and subjecting the mixture of swollenrubber particles and waterlogged particles to the separating action of aliquid containing asuitable soluble material to illcrease its specificgravity; substantially as described.

19. In the art of separating particles of rubber from mixtures in whichthey are contained, the method of increasing the buoyancy of the rubberparticles and of effecting their separation, which consists insubjecting them to the swelling action of a specificgravity loweringintumescent at a relatively low temperature (say from 60 to 100 E), andthen subjecting the mass to gravity separation in a liquid;substantially as described.

20. The method of separating particles of rubber from the guayule andother rubber bearing plants, which consists in subjecting the plant whenin'a finely divided condition, to the action'of a substance having aswelling and specific-gravity lowering effect upon separation of theswollen rubber particles by flotation; substantially as described.

21. The method of separating particles of rubber from the guayule shruband other rubber-bearing plants, which consists in subjec ting the plantwhen in a finely divided condition, to attrition in the presence of asubstance having a swelling and specificgravity lowering eti'ect uponthe rubber particles, and then effecting the separation of the swollenparticles of rubber by flotation; substantially as described.

22. The method of separating particles of rubber from the guayule andother rubberbearing plants, which consists in subjecting the plant whenin a finely divided condition, to agitation in a body of water and inthe presence of a substance having a swelling and specific-gravitylowering effect upon the rubber particles, and then effecting theseparation of the swollen particles of rubber by 23. The method ofseparating particles of rubber from the guayuleshrub and otherrubber-bearing plants, which consists in subjecting the plantwhen in afinely divided condition, to attrition in a body of water and in thepresence of a substance having a swelling and specific gravity loweringeffect upon the rubber particles, and then effecting the separation ofthe swollen particles of rubber by flotation; substantially as de--scribed.

24:. The method of separating particles of rubber from; the guayuleshrub and other rubber-bearing plants, which consists in subjecting theplant when in a finely divided condition, to attrition in a body ofwater and vto gravity separation of the same, then subjecting thelighter particles to a. substance having a swelling and specific-gravitylowering effect upon the rubber particles, and then effecting theseparation of the swollen particles of rubber by flotation;substantially asdescribed.

25. The method of separating particles of rubber from'the guayule andother rubber bearing plants, which consists in subjecting the plant whenin a finely divided condition, to the action of a petroleum distillateuntil the particles of rubber are swollen, and then effecting theseparation of the swollen particles of rubber by flotation substantiallyas described.

The method of separating particles of rubber from the guayule and otherrubber bearing'plants, which consists in subjecting the plant when in afinely divided condition,

to attrition in the presence of a petroleum distillate until theparticles of rubber are swollen, and then effecting the separation ofthe swollen particles of rubber by flotation; substantially asdescribed.

27. The method of separating particles of rubber from particles of wood,bark and resin, with which they are associated in the comminuted guayuleplant, the bagasse thereof, and the like, which consists in subjectingthe mixture to the action of a substance which has a greater buoyanteffect upon rubber than uponrcsin, but which is a sufficient solvent ofresin to soften the resin, effecting the separation of the swollenrubber particles by flotation, and briqu'eting the mass after theseparation of the swollen particles of rubber; substantially asdescribed.

In testimony whereof I afiix my signature, in presence of two witnesses.

HAROLD T. G. VAN DER LINDE. I'Vitnesses J. A. lVHrrcoMn, L. B; PENFIELD.

